The present invention relates to fluid-coupling devices of the type including both fluid operating chamber and a fluid reservoir chamber, and specifically to the providing a more efficient pumping mechanism for removing fluid from the operating chamber.
Although the present invention may be used advantageously in fluid-coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine, and will be described in connection therewith.
Fluid-coupling devices (“fan drives”) of the viscous shear type have been popular for many years for driving engine cooling fans, primarily because their use results in substantial saving of engine horsepower. The typical fluid-coupling device operates in the engaged, relatively higher speed condition only when cooling is needed, and operates in a disengaged, relatively lower speed condition when little or no cooling is required. These devices typically use integrally formed wipers to control the amount of viscous fluid exiting the working chamber to control the relative engagement of the fan drive at a given input speed. Electronically controlled fan drives achieve a very low disengaged fan speed by removing nearly all the viscous fluid from the fan drive labyrinth, or working chamber, during disengaged operations. This is desirable in that it minimizes parasitic power losses in the vehicle while improving fuel economy.
However, these systems are known to have less damping and are prone to troublesome vibration. Countermeasures used to combat this problem are to use a relatively loose fan drive bearing and to operate with higher than normal axial clearances between the clutch plate (rotor) and the housings (cover and body). This allows the clutch and housing to move relatively independently when the system is in resonance, reducing vibration amplitude. In most conventional fan drive systems, the wiper is located adjacent to an axial face of the clutch. However, locating the wiper here on the fan drive typically results in contact between the clutch and wiper during resonance that is unacceptable.
To combat this resonance problem, some fan drive systems have provided a wiper that is located within the radial clearance between the clutch and the housing. This wiper is thus generically known as an OD wiper, or outer diameter wiper. However, leakage paths near the wiper due to the large axial internal clearances between the cover, clutch and body are the primary culprit affecting robust performance of these types of fan drives.